Nonspecific granulomatous prostatitis (NSGP) is a relatively uncommon type of chronic inflammation of the prostate, frequently mistaken for carcinoma on digital rectal examination, trans-rectal ultrasound (TRUS) and serum PSA test. It is presently the most frequent variety of granulomatous prostatitis observed at histological examination. The present study reviews the trans-rectal US results and serum PSA levels of 20 patients with biopsy-proven NSGP. Physical findings, laboratory data and US indicated malignancy in all cases. Sonographically (TRUS), the lesions appeared as single or multiple hypoechoic nodules, mainly localised in the peripheral zone of the gland, mimicking carcinoma. Mean serum PSA values were 13.3 ng/ml (range from 3.5 to 34 ng/ml), and only one patient had a value lower than 4 ng/ml. A sufficiently long period of follow-up (mean 19 months; range from 7 to 48 months) with TRUS and PSA was only possible in 11/20 patients. In 8/11 cases, serum PSA returned within normal range, and in 5/11 patients the US features slowly resolved, the hypoechoic nodules disappearing. Final diagnosis can only be obtained by prostatic biopsy. Several questions remain unanswered regarding the relationship between chronic prostatitis and prostatic carcinoma, natural history, the need for specific therapy and also the follow-up of this disease.